A new study in San Francisco indicates that pregnant women, especially those from low-income and Latino families, have widespread exposure to environmental pollutants and many chemicals are absorbed at greater levels by fetuses than by the pregnant women.

The findings, by researchers at the University of California, Berkeley, the University of California, San Francisco, and Biomonitoring California, derived from testing of maternal blood samples collected from 77 pregnant women at Zuckerberg San Francisco General Hospital from 2010 to 2011 and of umbilical cord blood samples from 65 of these women once they delivered their babies.

Published on Tuesday in the print edition of the journal Environmental Science and Technology, the study is the first in the United States to measure exposure to 59 toxic chemicals in pregnant women and their newborns.

The researchers measured polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs), mercury and lead, among other chemicals. These industrial pollutants are common in the environment, and in previous studies many have been detected in greater than 99 percent of US pregnant women, according to National Health and Nutrition Examination Survey (NHANES) data.

"Pregnant women in the US are exposed to many harmful industrial chemicals that have been linked to premature birth, low birth weight and birth defects, but estimates of how efficiently pollutants are transferred from mother to fetus have varied widely," Tracey Woodruff, a professor in the Department of Obstetrics, Gynecology and Reproductive Sciences and the Philip R. Lee Institute for Health Policy Studies at UCSF, was quoted as saying in a news release.

In the new study, of those samples tested for all 59 chemicals, the median number was 25 in maternal blood and 17 in umbilical cord blood; and eight of the 59 chemicals analyzed were detected in more than 90 percent of both the maternal and cord blood samples.

In addition, almost 80 percent of the chemicals detected in maternal blood samples were also detected in the umbilical cord blood samples, indicating that they passed through the placenta and entered the fetal environment, where they can pose a health risk to the developing baby. For those chemicals detected in at least 20 paired maternal and umbilical cord samples, 77 percent had significant correlations between maternal and umbilical cord concentrations.

"Contrary to previous research, we found evidence that several PCBs and OCPs were often higher in umbilical cord samples than in maternal blood samples," said lead author Rachel Morello-Frosch, a professor in the Department of Environmental Science, Policy and Management and the School of Public Health at UC Berkeley. The study also finds that concentrations of mercury and certain PBDEs were often higher in umbilical cord samples than in maternal samples, and for most PFCs and lead, cord blood concentrations were generally equal to or lower than maternal concentrations, which is consistent with previous research.

About the fetus' exposure to pollutants, Woodruff noted that it "may have significant consequences for the growing fetus, since many of these chemicals are known to affect development."

Of the women participating in this study, 95 percent had a combined annual household income of less than 40,000 US dollars, two-thirds were Latina and a third were born in Mexico, where they may have had less exposure to environmental toxics like the PBDEs found in flame retardants that have been widely used in the United States. "It is important for researchers to more fully understand chemical exposure trends among women of color, as well as immigrant and low-income women, as these populations are often understudied," Morello-Frosch said.